1. Field of the Invention
This invention relates to thickness shear piezoelectric oscillators and more particularly to a thickness shear pieoelectric oscillator comprising an elongate rectangular oscillating piece extending in a direction producing a thickness shear displacement and provided at its both ends with a tapered bevel portion, the oscillating piece being supported at upper and lower node points of the bevel portion.
2. Description of the Prior Art
In the above described kind of thickness shear piezoelectric oscillator, it has been the common practice to use such a support construction that an elongate oscillating piece, for example, an elongate crystal piece extends in a direction producing a thickness shear displacement, that is, in an X direction and that the oscillating piece is supported at its both end surfaces by a supporting means for the purpose of obtaining a temperature characteristic at which an excellent resonance frequency is produced. But, in order to make leakage of the oscillation at the supporting points small so as to make a series resonance resistance value (hereinafter will be called as R.sub.1 value) small and to obtain a large Q value, a ratio of a length of the oscillating piece to a thickness thereof is required to be the order of 30 to 100, thereby rendering the oscillating piece large in size. In addition, the crystal piece is provided at its both ends with an inclined surface, spherical surface or conical surface portion (hereinafter will be called as a bevel portion). Such bevel portion causes the thickness shear oscillation displacement to concentrate into the center part of the oscillating piece and to be reduced at both ends thereof. As a result, it is possible to make the R.sub.1 value somewhat small. But, even though the bevel portion is subjected to the working operation, the good oscillation characteristics could not be obtained unless the above mentioned ratio of the length of the oscillating piece to the thickness thereof is larger than the order of 25. Particularly, it is very difficult to make the conventional thickness shear piezoelectric oscillator small in size to an extent which is adapted to be used for a wrist watch and materialization of such small oscillator has long been awaited in the art.